Tag Archives: QRP

After completing a 6-band SSB/CW QRP transceiver (Summit Prowler IV) I found myself thinking about a more compact QRP SSB/CW rig for SOTA, with two of the main day-time SOTA HF bands (40/20m). The design driver this time was to try a different ‘form factor’ — I wanted a rig with a narrow and long case, such that it would easily slide inside a backpack, and on a summit sit vertically against a rock or be hand held. All my SOTA rigs so far use both front and back panels for connections and controls, so they need to sit level on a horizontal surface. As most rocks or tree stumps are low, you can’t easily read the display. Some designers get around this by putting the display on the top of the box, a sensible adaptation but one that makes the rig look like a flounder. Because I spend a lot of time building and using these radios at home on the shack bench as well as on a summit, I wanted a design for use in both situations.

Eamon EI9GQ’s book (‘Building a Transceiver’, RSGB 2018) started me down the path of another modular transceiver project. For this build I wanted to continue working with surface mount but without the compulsion to pack it all in tight. More space and the freedom to replace a module later. It would be a Shack Sloth rig (a base station), not a Summit Prowler, so the space, weight and power budget shackles fell off from the start.

Remembrance Day Contest is a 24 hour amateur radio operating contest conducted each year by the Wireless Institute of Australia, to commemorate those Australian licensed amateur radio operators who lost their lives in World War 2. It is ‘designed to encourage friendly participation and help improve the operating skills of participants‘, and is held on the weekend closest to the 15th August, the date on which hostilities ceased in the southwest Pacific. This year it commenced at 1pm local time on Saturday August 11th.

Last year I cross country ski’d into Federation Range VK3/VN-029, 1490 meters above sea level, activated it for 8 points (+3 winter bonus points) and ski’d out again. This is possible because this summit is just off groomed cross country ski tracks at Lake Mountain, ninety minutes north east of Melbourne, a popular sight-seeing, tobogganing and cross country skiing spot. Time to do it again. After picking up skis at Marysville I took Royston Trail from the car park up the long incline, to Panorama, then Hut Trail to Boundary Hut, the remains of a hiking hut, long since burned out, only the stone walls standing to waist height. Distance out is about 4km.

How could a GPS unit integrated with a SOTA transceiver assist in activations? I’ve been turning that thought over for a while now after seeing David VK5KK’s GPS and Arduino based grid square locator (posted to the ‘VK Homebrew’ group on facebook). The ready availability of cheap GPS units with a simple serial interface makes the option straight-forward. As my homebrew rigs are using Arduino Nanos and si5351 breakout boards, the GPS is just another (serial) attachment.

‘Summit Prowler IV’ is a scratch-built six-band SSB and CW transceiver, designed for portable and SOTA activations. It is based on Leon VK2DOB’s MST3 (Minimal Sideband Transceiver, third version) from 2016, with alterations to support multiple bands, my Arduino-based digital VFO/controller and keyer, and a few extras to support portable operating. The transceiver is a conventional single-conversion superhet with 12MHz IF and an si5351 and Arduino Nano-based digital VFO. This project comes after having done more than 50 activations with my 2013 MST Mk I kit radio on 40m SSB. This rig has performed well on 40m SSB (and CW after I added it) and has launched my interest in SOTA activating, turning me into an occasional weekend ‘summit prowler‘.

Charlie ZL2CTM has been pushing out a series of excellent videos on his YouTube channel that take you through the circuit design, making and testing of superhet SSB transceiver modules. Yesterday my eyebrow involuntarily raised ever so slightly at his use of Veroboard as the substrate for his latest 8MHz crystal filter. Veroboard? At radio frequencies? Veroboard et les fréquences radio ne sont pas compatibles!

The Melbourne Cup, a hugely hyped horse race affords Melburnians with a three day long weekend, allowing yours truly, being disinterested in all things equestrian, a day in the Victorian mountains, my first activations for more than 3 months. Mt Torbreck VK3/VN-001 in the Rubicon Range just south of Eildon would start the day, followed by nearby Pyramid Hill and the peak in the Cathedral Ranges if time and energy allowed. Leaving Melbourne suburbs early, I turned the ignition key at 6:10am and drove towards Eildon, then south down Snobs Creek Rd to Conns Gap Rd, parking at Barnewall Plains Track by 0812, 2 hours and 2 minutes drive time. The temperature was 8.5C. The gate was open and a proper 4WD would have ploughed up the first steep section, but I happily walked the kilometer or so to the camping area then up the track to the summit. Steep, but with rewarding scenery, although the summit was in mist and just under cloud.

Having finished my latest Arduino Nano/si5351 VFO/BFO/Controller, I wanted to hook it up to some receiver stages to realise a SSB receiver. My grand plan for these modules is to build a multiband SSB/CW transceiver for SOTA and portable operation (another rig in my established ‘Summit Prowler’ series). The architecture will be a single conversion superhet with an IF of 12 MHz. For a base design I chose Leon VK2DOB’s MST3, a proven design which I am very familiar with, having used the MST (circa 2013) on nearly all of my SOTA activations to date.

I scratch-built two boards. The first is the MST3 product detector (SA612), audio filter (NE5534) and audio amplifier (TDA7052A). This module includes receiver muting, sidetone injection and audio-derived AGC which controls the gain of the TDA7052A. The second board contains the transmit and receive mixers (both SA612s), some SA630D RF switches to switch the bandpass filter between transmit and receive signal paths, as well as two 5-pole crystal filters (one for SSB, one for CW), each switched by another pair of SA630Ds. There is no IF gain stage, although I put some pads on the end of this board for one or two MOSFET stages, if needed.

As per other recent scratch building efforts these boards are a curious jumble of thru-hole and SOIC ICs, soldered to the copper side of a Muppet style hand drawn and etched board, largely populated with junk box and surplus sales components.

Once the boards were debugged, temporarily adding a 40m bandpass filter and connecting the VFO/BFO up brought the little receiver to life. I used no si5351 clock filtering or buffering, just CLK0 and CLK2 square waves straight into the SA612 Gilbert cell active mixers, which have some useful gain. The sound of the receiver is pleasant, to me at least. The video includes a range of DX and local signals on 40m from my QTH in the north-eastern suburbs of Melbourne, received over a day.Next, I will add a third board with a bank of switched bandpass filters and switching logic, all controlled by the Arduino. More to follow.

Back in February 2017 I scratch-built my first Arduino and si5351 VFO. Here’s my second one. It is a generic Nano/si5351 module wired up to Farhan’s Raduino circuit. The si5351 is on an Adafruit breakout which includes a 3.3v regulator and crystal. Everything else is as per Raduino other than the presence of a second 7805 regulator for the LCD (and a 1000uF electrolytic storage capacitor) which will allow testing of Pavel CO7WT’s scheme for saving the VFO frequency to the Arduino’s EEPROM when the power drops.